Due to rapidly increasing traffic in optical communications in recent years, the transmission capacity of presently used single-core optical fibers is approaching its limit. So, as a means to further expand the communication capacity, multicore fibers in which a plurality of cores are formed in one fiber have been proposed. Use of multi-core fibers can suppress the laying cost of optical fibers and expand the transmission capacity.
When a multi-core fiber is used as a transmission path, each of the core parts of the multicore fiber needs to be connected to another multi-core fiber, an optical element, or the like respectively to send and/or receive transmission signals. A multi-core connector, in particular, including a plurality of such multi-core fibers can easily connect a plurality of multi-core fibers altogether.
On the other hand, a multi-core fiber has cores arranged at positions other than the center of the cross section, and thus the arrangement of cores of a multi-core fiber has an orientation in a rotation direction with the center axis of the multi-core fiber as a rotational axis. Thus, for connecting a multi-core fiber, rotational alignment of the multi-core fiber with its connection target is required.
As a method for specifying the arrangement of cores in a multi-core fiber, Patent Document 1 discloses a multi-core fiber having a non-circular cross section.
Also, as a connector using a multi-core fiber, Patent Document 2, for example, discloses a connector in which positioning in rotational direction is considered.